阅读说明：本技术 液压驱动装置 (Hydraulic drive device ) 是由 伊藤和裕 沼口和弘 于 2019-11-22 设计创作，主要内容包括：背压阀(71L)以位于方向控制阀(23)与液压马达(32L)之间的方式设于一对供排管路(25A、25B)的中途。背压阀(71L)基于供排管路(25A、25B)的压力差来使阀柱(72L)沿轴向位移。背压阀(71L)具备连通路(73L),若阀柱(72L)的位移因供排管路(25A、25B)之间的压力差而超过预定量(X-(CM)),则该连通路(73L)将供排管路(25A、25B)之间连通。连通路(73L)设于背压阀(71L)的阀柱(72L)。(The back pressure valve (71L) is provided midway between the pair of supply and discharge lines (25A, 25B) so as to be positioned between the directional control valve (23) and the hydraulic motor (32L). The back pressure valve (71L) displaces a spool (72L) in the axial direction on the basis of the pressure difference between the supply and discharge lines (25A, 25B). The back pressure valve (71L) is provided with a communication passage (73L) and exceeds a predetermined amount (X) when the displacement of the spool (72L) is caused by the pressure difference between the supply and discharge lines (25A, 25B) CM ) The communication passage (73L) communicates the supply and discharge pipes (25A, 25B). The communication passage (73L) is provided in a spool (72L) of the back pressure valve (71L).)

1. A hydraulic drive device is provided with:

a first hydraulic pump and a second hydraulic pump;

a first hydraulic motor that is rotationally driven by pressure oil from the first hydraulic pump;

a second hydraulic motor that is rotationally driven by pressure oil from the second hydraulic pump;

a pair of first and second supply/discharge passages connecting the first hydraulic pump and the hydraulic oil tank to the first hydraulic motor;

a pair of third and fourth supply/discharge passages connecting the second hydraulic pump, the hydraulic oil tank, and the second hydraulic motor;

a first directional control valve provided in the middle of the first and second supply/discharge passages and switching a direction of pressure oil supplied and discharged between the first hydraulic pump and the hydraulic oil tank and the first hydraulic motor;

a second directional control valve provided in the middle of the third and fourth supply/discharge passages and switching the direction of pressure oil supplied and discharged between the second hydraulic pump and the hydraulic oil tank and the second hydraulic motor;

a first back pressure valve provided midway between the first supply/discharge passage and the second supply/discharge passage so as to be positioned between the first directional control valve and the first hydraulic motor, the first back pressure valve displacing the first spool in the axial direction based on a pressure difference between the first supply/discharge passage and the second supply/discharge passage; and

a second back pressure valve provided midway between the third supply/discharge passage and the fourth supply/discharge passage so as to be positioned between the second directional control valve and the second hydraulic motor, the second back pressure valve displacing the second spool in the axial direction based on a pressure difference between the third supply/discharge passage and the fourth supply/discharge passage,

the above-described hydraulic drive apparatus is characterized in that,

the first back pressure valve includes a first communication passage that communicates between the first supply/discharge passage and the second supply/discharge passage when a displacement of the first spool exceeds a predetermined amount due to a pressure difference between the first supply/discharge passage and the second supply/discharge passage,

the second back pressure valve includes a second communication passage that communicates between the third supply/discharge passage and the fourth supply/discharge passage when displacement of the second spool exceeds a predetermined amount due to a pressure difference between the third supply/discharge passage and the fourth supply/discharge passage.

2. Hydraulic drive arrangement according to claim 1,

the first communication passage is provided in the first spool of the first back pressure valve,

the second communication passage is provided in the second spool of the second back pressure valve.

3. Hydraulic drive arrangement according to claim 1,

a first orifice that restricts a flow rate of the pressure oil flowing through the first communication passage is provided in a middle of the first communication passage,

a second orifice that restricts a flow rate of the pressure oil flowing through the second communication passage is provided in a middle of the second communication passage,

the first and second restrictors are set to suppress a difference between a flow rate of the pressure oil flowing between the first hydraulic pump and the first hydraulic motor and a flow rate of the pressure oil flowing between the second hydraulic pump and the second hydraulic motor in a state where both the first hydraulic motor and the second hydraulic motor are rotating.

Technical Field

The present disclosure relates to a hydraulic drive device used for a construction machine such as a hydraulic excavator including a hydraulic motor.

Background

In general, a hydraulic excavator as a typical example of a construction machine includes: a lower traveling body capable of traveling by itself; an upper revolving structure rotatably mounted on the lower traveling structure; and a working device provided on the front side of the upper slewing body. The lower traveling structure is configured to include, for example: an endless track; and a left and right driving device including a hydraulic motor for driving the crawler to rotate around. Here, the rotation speed R of the travel drive device can be expressed by the following equation 1 using the discharge flow rate Qp of the hydraulic pump and the capacity Vm of the hydraulic motor. The added word "p" indicates a pump, and the added word "m" indicates a motor.

[ mathematical formula 1]

Therefore, the rotation speed RL of the left travel drive device is determined by the discharge flow rate Qp1 (hereinafter, also simply referred to as pump discharge flow rate Qp1) of one of the hydraulic pumps that supplies the pressure oil to the left travel drive device and the displacement VmL (hereinafter, also simply referred to as motor displacement VmL) of the hydraulic motor in the left travel drive device. The rotation speed RR of the right travel drive device is determined by the discharge flow rate Qp2 (hereinafter, also simply referred to as a pump discharge flow rate Qp2) of the other hydraulic pump that supplies pressure oil to the right travel drive device and the displacement VmR (hereinafter, also simply referred to as a motor displacement VmR) of the hydraulic motor in the right travel drive device. Therefore, the rotation speed RL of the left travel drive device and the rotation speed RR of the right travel drive device may differ depending on the pump discharge flow rates Qp1 and Qp2 and the motor capacities VmL and VmR. In the present specification and the drawings, in order to distinguish between the left and right, a variable, a symbol, or the like corresponding to "left" may be denoted by "L", and a variable, a symbol, or the like corresponding to "right" may be denoted by "R".

When the hydraulic excavator travels on a flat ground, if a difference occurs in the rotation speeds RL and RR of the left and right travel drive devices, the hydraulic excavator may curve. In order to prevent such meandering during traveling on flat terrain, it is conceivable to perform the straight-ahead correction in synchronization with the rotation speeds RL and RR of the left and right travel driving devices, for example. For example, patent document 1 describes the following technique: a bypass throttle circuit for straight-ahead correction having a variable throttle is provided in a circuit for supplying pressure oil to a hydraulic motor for traveling, and straight-ahead correction is performed.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open publication No. 2005-119619

Disclosure of Invention

In the technique described in patent document 1, since the opening of the throttle during traveling is constant, control or adjustment such as reduction of the throttle of the traveling drive device on the low rotation side cannot be performed when meandering occurs, and the effect of the straight-ahead correction may not be sufficiently exhibited. In the technique of patent document 1, since the inlet/outlet oil passage of the driving device for traveling is connected to the bypass throttle circuit, a constant flow rate is always returned to the tank regardless of the traveling state, and the efficiency may be lowered. Further, in the technique of patent document 1, when the bypass throttle circuit is provided in the vicinity of the driving device for running, the backflow of the oil may occur on the motor drain circuit side due to the pressure loss of the drain pipe in the center joint. In this case, the motor discharge pressure may increase, which may reduce the durability of the motor seal. Further, a work of correcting the throttle is required, and this work may be complicated. Further, since the bypass throttle circuit and the communication pipe need to be newly provided, there is a possibility that the cost may be increased. In addition, when a communication oil passage is provided in the driving device for running, if the communication oil passage is always opened, the braking performance and the starting performance may be affected. Further, if the number of components is increased in the driving device for traveling, the driving device for traveling may be increased in size.

An object of one embodiment of the present invention is to provide a hydraulic drive device that can suppress hunting of travel due to a difference in the rotational speed between a left travel drive device (first hydraulic motor) and a right travel drive device (second hydraulic motor) at an appropriate timing.

One embodiment of the present invention provides a hydraulic drive device including: a first hydraulic pump and a second hydraulic pump; a first hydraulic motor that is rotationally driven by pressure oil from the first hydraulic pump; a second hydraulic motor that is rotationally driven by pressure oil from the second hydraulic pump; a pair of first and second supply/discharge passages connecting the first hydraulic pump and the hydraulic oil tank to the first hydraulic motor; a pair of third and fourth supply/discharge passages connecting the second hydraulic pump, the hydraulic oil tank, and the second hydraulic motor; a first directional control valve provided in the middle of the first and second supply/discharge passages and switching a direction of pressure oil supplied and discharged between the first hydraulic pump and the hydraulic oil tank and the first hydraulic motor; a second directional control valve provided in the middle of the third supply/discharge passage and the fourth supply/discharge passage and configured to switch a direction of pressure oil supplied and discharged between the second hydraulic pump and the hydraulic oil tank and the second hydraulic motor; a first back pressure valve provided midway between the first supply/discharge passage and the second supply/discharge passage so as to be positioned between the first directional control valve and the first hydraulic motor, the first back pressure valve displacing the first spool in the axial direction based on a pressure difference between the first supply/discharge passage and the second supply/discharge passage; and a second back pressure valve provided midway between the third supply/discharge passage and the fourth supply/discharge passage so as to be positioned between the second directional control valve and the second hydraulic motor, the second back pressure valve displacing the second spool in the axial direction based on a pressure difference between the third supply/discharge passage and the fourth supply/discharge passage, in the hydraulic drive apparatus, the first back pressure valve includes a first communication passage, and when a displacement of the first spool exceeds a predetermined amount due to a pressure difference between the first supply/discharge passage and the second supply/discharge passage, the first communication passage communicates between the first supply/discharge passage and the second supply/discharge passage, and the second back pressure valve includes a second communication passage that communicates between the third supply/discharge passage and the fourth supply/discharge passage when the displacement of the second spool exceeds a predetermined amount due to a pressure difference between the third supply/discharge passage and the fourth supply/discharge passage.

According to one embodiment of the present invention, it is possible to suppress hunting of travel due to a difference in the rotational speed between the first hydraulic motor (for example, the left-side travel drive device) and the second hydraulic motor (for example, the right-side travel drive device) at an appropriate timing.

Drawings

Fig. 1 is a front view of a hydraulic excavator according to an embodiment.

Fig. 2 is a hydraulic circuit diagram of the hydraulic excavator in fig. 1.

Fig. 3 is a hydraulic circuit diagram enlarging a portion (III) in fig. 2.

Fig. 4 is a hydraulic circuit diagram enlarged from the portion (IV) in fig. 3.

Fig. 5 is a longitudinal sectional view of the back pressure valve of the embodiment in which the spool stroke is at the 0 position (neutral position) in fig. 8.

FIG. 6 is a view showing the stroke of the spool as X in FIG. 8_EOThe position (the notch final position, the position before the start of the full-periphery oil passage) shows a longitudinal sectional view of the back pressure valve.

FIG. 7 is a view showing the stroke of the spool as X in FIG. 8_FSPosition (full position) shows a longitudinal section of the back pressure valve.

FIG. 8 shows "spool stroke X" of the back pressure valve and "opening area A of the outlet oil passage_CBAnd the opening area A of the communication path_CM"is an example of the relationship.

Fig. 9 is a characteristic diagram showing an example of the relationship between the "drive pressure P" and the "spool stroke X" of the back pressure valve.

Fig. 10 is a characteristic diagram showing an example of the relationship between the "drive pressure P" and the "communication flow rate Q".

Fig. 11 is a schematic diagram showing a meandering suppressing operation according to the embodiment.

Fig. 12 is a characteristic diagram showing an example of temporal changes in the "rotation speed R", "drive pressure P", "stroke X", and "communication flow rate Qt" in the embodiment.

Fig. 13 is a longitudinal sectional view of a back pressure valve according to a modification example in which a spool stroke is a neutral position (0 position).

FIG. 14 shows the spool stroke as the full stroke position (X)_FSPosition) shows a longitudinal section of the back pressure valve.

Fig. 15 is a schematic diagram showing a meandering operation of the comparative example.

Fig. 16 is a characteristic diagram showing an example of temporal changes in the "rotation speed R", "drive pressure P", and "stroke X" of the comparative example.

Detailed Description

Hereinafter, a case where the hydraulic drive device according to the embodiment of the present invention is applied to a hydraulic drive device (hydraulic drive device for traveling) of a construction machine (hydraulic excavator) will be described with reference to the drawings as an example.

Fig. 1 to 12 show an embodiment. In fig. 1, a hydraulic excavator 1 as a typical example of a construction machine (work vehicle) includes: a self-propelled crawler-type lower traveling body 2; a swing device 3 provided on the lower traveling structure 2; an upper revolving structure 4 rotatably mounted on the lower traveling structure 2 via a revolving device 3; and a working mechanism 5 of a multi-joint structure provided on the front side of the upper slewing body 4 and performing excavation work and the like.

At this time, the lower traveling structure 2 and the upper revolving structure 4 constitute a vehicle body of the hydraulic excavator 1. The working mechanism 5, which is also referred to as a working machine or a front body, includes, for example, a boom 5A, an arm 5B, a bucket 5C as a working tool, and a boom cylinder 5D, an arm cylinder 5E, and a bucket cylinder 5F as a working tool cylinder for driving them. The working device 5 can perform a pitching operation by extending or contracting the cylinders 5D, 5E, and 5F as hydraulic cylinders.

The lower carrier 2 includes: a frame 2A; driving wheels 2B arranged on the left and right sides of the frame 2A; a floating wheel 2C provided on the opposite side of the driving wheel 2B in the front-rear direction on both the left and right sides of the frame 2A; and a track 2D wound around the driving wheel 2B and the floating wheel 2C. The left and right driving wheels 2B (i.e., the left and right track belts 2D) are driven by traveling hydraulic motors 32L and 32R (see fig. 2) of the left and right traveling drive devices 31L and 31R, which will be described later.

The upper slewing body 4 is mounted on the lower traveling body 2 via a slewing device 3, and the slewing device 3 includes a slewing bearing, a hydraulic motor for slewing, a speed reduction mechanism, and the like. The upper slewing body 4 is configured to include: a revolving frame 6 serving as a support structure (base frame) of the upper revolving structure 4; and a cab 7, a counterweight 8, and the like mounted on the revolving frame 6. In this case, an engine 12, hydraulic pumps 13, 14, and 20, a hydraulic oil tank 15, a control valve device 22 (see fig. 2), and the like, which will be described later, are mounted on the revolving frame 6.

Revolving frame 6 is attached to lower traveling structure 2 via revolving device 3. A cab 7 having an operating room therein is provided on the front left side of the revolving frame 6. An operator seat on which an operator sits is provided in the cab 7. An operation device 27 for operating the hydraulic excavator 1, a tilt/swivel change-over switch 60 (see fig. 2), and the like are provided around the driver's seat. The operation device 27 outputs a pilot signal (pilot pressure) according to an operation (lever operation, pedal operation) of the operator to the control valve device 22. Thus, the operator can operate (drive) the traveling hydraulic motors 32L and 32R (see fig. 2) of the traveling drive devices 31L and 31R, the cylinders 5D, 5E, and 5F of the working device 5, and the turning hydraulic motor of the turning device 3.

A controller 61 (see fig. 2) described later is provided in the cab 7 so as to be positioned on the lower side behind the driver's seat. On the other hand, a counterweight 8 for balancing the weight of the working device 5 is provided on the rear end side of the revolving frame 6.

Hereinafter, a hydraulic drive device for driving the hydraulic excavator 1 will be described with reference to fig. 2 to 12 in addition to fig. 1.

As shown in fig. 2, hydraulic excavator 1 includes a hydraulic circuit 11 that operates (drives) hydraulic excavator 1 based on pressure oil supplied from hydraulic pumps 13 and 14. The hydraulic circuit 11 constituting the hydraulic drive device includes an engine 12, hydraulic pumps 13, 14, and 20, a hydraulic oil tank 15, a center joint 19, a control valve device 22, an operation device 27, travel drive devices 31L and 31R, a controller 61, and the like. In order to avoid the drawing from becoming complicated, the hydraulic circuit 11 shown in fig. 2 is mainly illustrated as a circuit for causing the lower traveling structure 2 to travel (i.e., a hydraulic drive device for traveling). In other words, the hydraulic circuit 11 shown in fig. 2 omits a circuit for driving the working mechanism 5 (i.e., a hydraulic drive mechanism for working) and a circuit for driving the slewing device 3 (i.e., a hydraulic drive mechanism for slewing the upper slewing body 4 relative to the lower traveling body 2).

Engine 12 is mounted on revolving frame 6. The engine 12 is constituted by an internal combustion engine such as a diesel engine. A first hydraulic pump 13, a second hydraulic pump 14, and a pilot hydraulic pump 20 are mounted on the output side of the engine 12. These hydraulic pumps 13, 14, 20 are rotationally driven by the engine 12. The drive source (power source) for driving the hydraulic pumps 13, 14, and 20 may be constituted by the engine 12 alone, which is an internal combustion engine, or may be constituted by the engine and the electric motor, or the electric motor alone, for example.

The first hydraulic pump 13 and the second hydraulic pump 14 (hereinafter also referred to as hydraulic pumps 13 and 14) are mechanically (i.e., power transmittable) connected to the engine 12. The hydraulic pumps 13, 14 are main hydraulic pumps of the hydraulic circuit 11. The hydraulic pumps 13, 14 are constituted by, for example, variable displacement swash plate type, swash shaft type, or radial piston type hydraulic pumps. The hydraulic pumps 13 and 14 are connected to traveling hydraulic motors 32L and 32R, turning hydraulic motors, and cylinders 5D, 5E, and 5F (hereinafter also referred to as hydraulic actuators 5D to 32R) serving as hydraulic actuators via a control valve device 22.

Here, the first hydraulic pump 13 supplies pressure oil to the traveling hydraulic motor 32L (hereinafter, also referred to as a left traveling hydraulic motor 32L) of the left traveling drive device 31L (hereinafter, also referred to as a left traveling drive device 31L) of the hydraulic excavator 1 in common. Although not shown, the first hydraulic pump 13 supplies pressure oil to, for example, a hydraulic motor for turning, the boom cylinder 5D, and the arm cylinder 5E. As shown in fig. 2, the first hydraulic pump 13 discharges the hydraulic oil stored in the hydraulic oil tank 15 to the first discharge line 16 as pressure oil. The pressure oil discharged to the first discharge line 16 is supplied to the left travel hydraulic motor 32L via the control valve device 22 and the center joint 19. The pressure oil supplied to the left travel hydraulic motor 32L is returned to the hydraulic oil tank 15 via the center joint 19, the control valve device 22, and the return line 17. Thereby, the working oil circulates.

On the other hand, the second hydraulic pump 14 is the same as the first hydraulic pump 13. The second hydraulic pump 14 supplies pressure oil in common to a travel hydraulic motor 32R (hereinafter, also referred to as a right travel hydraulic motor 32R) of a travel drive device 31R on the right side of the hydraulic excavator 1 (hereinafter, also referred to as a right travel drive device 31R). Although not shown, the second hydraulic pump 14 supplies pressure oil to, for example, the boom cylinder 5D and the bucket cylinder 5F. As shown in fig. 2, the second hydraulic pump 14 discharges the hydraulic oil stored in the hydraulic oil tank 15 to the second discharge pipe 18 as pressure oil. Thereby, the working oil circulates.

Center joint 19 is provided between lower traveling structure 2 and upper revolving structure 4. The center joint 19 allows the oil (working oil, pressure oil) to flow between the upper slewing body 4 and the lower traveling body 2 regardless of the slewing motion of the upper slewing body 4 with respect to the lower traveling body 2.

The pilot hydraulic pump 20 as a pilot pump is mechanically connected to the engine 12, similarly to the hydraulic pumps 13 and 14. The pilot hydraulic pump 20 is constituted by, for example, a fixed displacement type gear pump. The pilot hydraulic pump 20 discharges the hydraulic oil stored in the hydraulic oil tank 15 into the pilot discharge pipe line 21 as pressure oil. That is, the pilot hydraulic pump 20 and the hydraulic oil tank 15 together constitute a pilot hydraulic pressure source.

The pilot hydraulic pump 20 supplies pressurized oil (hereinafter, also simply referred to as a shift pilot pressure) to the tilt switching valves 51 and 51 of the hydraulic motors 32L and 32R for traveling via a pilot control valve 58, which will be described later. The pilot hydraulic pump 20 supplies pressure oil (hereinafter, also simply referred to as pilot pressure for operation) to (the directional control valves 23, 24 of) the control valve device 22 via (the travel lever/pedal operation devices 28, 29 of) the operation device 27.

The control valve device 22 is a control valve group including a plurality of directional control valves 23 and 24. The control valve device 22 shown in fig. 2 is mainly illustrated by the directional control valves 23 and 24 for traveling, that is, the left directional control valve 23 and the right directional control valve 24 for traveling. In other words, the control valve device 22 shown in fig. 2 omits a directional control valve for operation (a boom directional control valve, an arm directional control valve, and a bucket directional control valve), and a directional control valve for turning. Similarly, the operating device 27 shown in fig. 2 is also shown by the operating devices 28 and 29 for traveling, that is, the left traveling lever-pedal operating device 28 and the right traveling lever-pedal operating device 29. In other words, the operation device 27 shown in fig. 2 omits a lever operation device (left lever operation device, right lever operation device) for work.

The control valve device 22 distributes the pressure oil discharged from the hydraulic pumps 13, 14 to the hydraulic actuators 5D-32R. That is, the control valve device 22 controls the direction of the pressure oil supplied from the hydraulic pumps 13 and 14 to the hydraulic actuators 5D to 32R in accordance with a switching signal (pilot pressure for operation) of the operation device 27 disposed in the cab 7. Thus, the hydraulic actuators 5D to 32R are driven by the pressure oil (hydraulic oil) supplied (discharged) from the hydraulic pumps 13 and 14.

Here, the left travel direction control valve 23 of the control valve device 22 is provided midway between the pair of pipes 25A, 25B, that is, midway between the first left supply/discharge pipe 25A serving as a first supply/discharge passage (first left supply/discharge passage) and the second left supply/discharge pipe 25B serving as a second supply/discharge passage (second left supply/discharge passage). The first left supply/discharge line 25A and the second left supply/discharge line 25B are connected between the first hydraulic pump 13 and the hydraulic oil tank 15, and the left travel hydraulic motor 32L. The left travel direction control valve 23 is formed of a pilot-operated direction control valve, for example, a hydraulic pilot-operated direction control valve having a 4-port 3 position (or a 6-port 3 position). The left travel directional control valve 23 switches supply and discharge of hydraulic oil to and from the left travel hydraulic motor 32L between the first hydraulic pump 13 and the left travel hydraulic motor 32L.

That is, the left travel direction control valve 23 as a first direction control valve switches the direction of pressure oil supplied and discharged between the first hydraulic pump 13 and the hydraulic oil tank 15 and the left travel hydraulic motor 32L. Thereby, the left traveling direction control valve 23 rotates the left traveling hydraulic motor 32L in the normal direction or in the reverse direction. The hydraulic pilot portions 23A, 23B of the left travel direction control valve 23 are supplied with switching signals based on the operation of the left travel lever-pedal operation device 28. Thereby, the left traveling direction control valve 23 is switched from the neutral position (a) to the switching positions (B) and (C).

The right travel direction control valve 24 of the control valve device 22 is provided midway between the pair of pipes 26A, 26B, that is, midway between a first right supply-and-discharge pipe 26A serving as a third supply-and-discharge passage (first right supply-and-discharge passage) and a second right supply-and-discharge pipe 26B serving as a fourth supply-and-discharge passage (second right supply-and-discharge passage). The first right supply/discharge line 26A and the second right supply/discharge line 26B are connected between the second hydraulic pump 14 and the hydraulic oil tank 15, and the right travel hydraulic motor 32R. The right travel directional control valve 24 as a second directional control valve switches the direction of pressure oil supplied and discharged between the second hydraulic pump 14 and the hydraulic oil tank 15 and the right travel hydraulic motor 32R, similarly to the left travel directional control valve 23. The hydraulic pilot portions 24A, 24B of the right travel direction control valve 24 are supplied with switching signals based on the operation of the right travel lever-pedal operation device 29.

The operation device 27 includes travel lever/pedal operation devices 28 and 29 (hereinafter, also simply referred to as travel operation devices 28 and 29) serving as travel operation devices and a work lever operation device (not shown) serving as a work operation device. The travel operation devices 28 and 29 are disposed in the cab 7 of the upper revolving structure 4, more specifically, in front of the driver's seat. The working lever operating devices are disposed on both left and right sides of the driver's seat. The travel operation devices 28 and 29 are, for example, lever-pedal type pressure reducing valve type pilot valves. The pressure oil from the pilot hydraulic pump 20 is supplied to the travel operation devices 28 and 29 through the pilot discharge pipe line 21. The travel operation devices 28 and 29 output switching signals corresponding to lever operations and pedal operations performed by the operator to the control valve device 22 (the directional control valves 23 and 24).

Here, the left travel operation device 28 switches the left travel directional control valve 23. That is, the left travel operation device 28 is operated by the operator to supply (output) the left travel pilot pressure, which is the operation pilot pressure (switching signal) in proportion to the operation amount thereof, to the hydraulic pilot portions 23A, 23B of the left travel direction control valve 23. This switches the switching position of the left travel direction control valve 23. On the other hand, the right travel operation device 29 switches the right travel directional control valve 24.

The left travel drive device 31L rotationally drives the left drive wheels 2B based on the pressure oil supplied from the first hydraulic pump 13. The left travel hydraulic motor 32L of the left travel drive device 31L is connected to the first hydraulic pump 13 and the hydraulic oil tank 15 via the first and second left supply and discharge lines 25A and 25B. A left travel direction control valve 23 is provided in the middle of the first and second left supply/discharge lines 25A, 25B.

As shown in fig. 3, the left travel drive device 31L (hereinafter, also simply referred to as the travel drive device 31L) is composed of a left travel hydraulic motor 32L (hereinafter, also simply referred to as the hydraulic motor 32L) and a left brake valve 44L (hereinafter, also simply referred to as the brake valve 44L). In this case, the driving device for traveling 31L is configured by connecting a brake valve 44L that controls the flow of the inlet and outlet ports (motor ports 47A and 47B) of the hydraulic motor 32L to the hydraulic motor 32L that is rotatable in both directions by reversing the inlet and outlet ports of the pressure oil.

The left travel hydraulic motor 32L as the first hydraulic motor is rotationally driven by the pressure oil from the first hydraulic pump 13. Here, the hydraulic motor 32L is constituted by a variable displacement hydraulic motor. More specifically, the hydraulic motor 32L is constituted by an axial piston swash plate type hydraulic motor having a swash plate 42 as a capacity variable portion. The hydraulic motor 32L includes, for example, an output shaft 34, a variable displacement mechanism 41, and the like. The hydraulic motor 32L can rotate the output shaft 34 by the pressure oil supplied from the hydraulic pump 13 and change the rotation speed of the output shaft 34 by the displacement variable mechanism 41.

The output shaft 34 is rotatably provided in a motor housing 33 forming a housing of the hydraulic motor 32L. The output shaft 34 is spline-coupled to a cylinder (not shown) and rotates integrally with the cylinder. A plurality of cylinders (not shown) are bored in the cylinder block so as to be separated in the circumferential direction and extend in the axial direction, and a piston (not shown) is slidably inserted into each cylinder. The piston reciprocates in the cylinder by rotation of the cylinder body. A valve plate (not shown) is provided between the motor housing 33 and the cylinder block. The valve plate has a pair of supply and discharge ports intermittently communicating with the cylinders of the cylinder block. The supply/discharge ports of the valve plate communicate with supply/discharge pipes 25A and 25B.

The capacity variable mechanism 41 is provided inside the motor housing 33. The variable displacement mechanism 41 includes a swash plate 42 as a variable displacement portion and a tilt actuator 43 as a variable displacement actuator. The variable displacement mechanism 41 changes the tilt angle of the swash plate 42 by the tilt actuator 43, thereby adjusting the displacement of the pressure oil supplied to each cylinder of the cylinder block and changing the rotation speed and the output torque of the output shaft 34.

The swash plate 42 always maintains a large tilt position by a resultant force of the pressing forces (pressing resultant force) acting from the pistons. In contrast, the swash plate 42 is pressed by the tilt actuator 43 to tilt to a small tilt position. In this case, when the swash plate 42 is in the large swash position, the stroke amount (stroke difference) of the pistons increases, and the output shaft 34 rotates at a low speed with a high torque. On the other hand, when the swash plate 42 is in the small tilt position, the supply flow rate (motor open capacity) required for rotation of the hydraulic motor 32L is reduced by reducing the stroke amount of the piston, and the output shaft 34 rotates at a high speed with a low torque.

The tilt actuator 43 drives the swash plate 42 of the hydraulic motor 32L to change the motor capacity. Here, the tilt rotation driver 43 includes: a tilt rotary cylinder 43A provided in the motor housing 33; and a tilt rotary piston 43B (servo piston) having a base end side slidably fitted in the tilt rotary cylinder 43A and a tip end side abutting against the back surface of the swash plate 42. The tilt piston 43B presses the back surface side of the swash plate 42 in accordance with the pressure oil supplied from the tilt switching valve 51 into the tilt cylinder 43A, whereby the tilt actuator 43 tilts the swash plate 42 between a large tilt position and a small tilt position and changes the rotation speed of the output shaft 34.

As shown in fig. 3, the brake valve 44L constitutes the travel drive device 31L together with the hydraulic motor 32L. The brake valve 44L has a pair of valve ports 45A, 45B, a pilot pressure port 46, a pair of motor ports 47A, 47B, a pair of check valves 48A, 48B, a left back pressure valve 71L, a high pressure selector valve 50, a tilt switching valve 51 as a capacity control valve, and a pair of relief valves 53A, 53B. The check valves 48A, 48B, the left back pressure valve 71L, the high pressure selector valve 50, the tilt switching valve 51, and the relief valves 53A, 53B are provided integrally with the motor case 33 of the hydraulic motor 32L, for example.

The valve ports 45A, 45B are open to the motor housing 33, for example. The valve ports 45A and 45B are connected to the hydraulic pump 13 or the hydraulic oil tank 15 according to the switching position of the directional control valve 23. The pilot pressure port 46 is opened in the motor housing 33, for example. The pilot pressure port 46 is connected to the pilot hydraulic pump 20 or the hydraulic oil tank 15 according to the switching position of the pilot pressure control valve 58. The motor ports 47A, 47B are connected to supply and discharge ports of a valve plate of the hydraulic motor 32L.

The check valves 48A and 48B are provided midway in the supply and discharge pipes 25A and 25B so as to be positioned between the hydraulic motor 32L and the directional control valve 23. The check valves 48A, 48B are check valves of a poppet type. The check valves 48A, 48B operate as follows: the pressure oil flowing from the valve ports 45A, 45B side to the motor ports 47A, 47B side is passed through, while the pressure oil flowing from the motor ports 47A, 47B side to the valve ports 45A, 45B side is shut off.

The left back pressure valve 71L is provided in the middle of the supply and discharge pipes 25A and 25B in parallel with the check valves 48A and 48B. That is, a left back pressure valve 71L (hereinafter, also simply referred to as a back pressure valve 71L) as a first back pressure valve is provided in the middle of the pair of supply and discharge lines 25A and 25B so as to be positioned between the directional control valve 23 and the hydraulic motor 32L. In the back pressure valve 71L, a left spool 72L (hereinafter, also simply referred to as a spool 72L) as a first spool is displaced in the axial direction based on the pressure difference between the supply and discharge lines 25A, 25B. That is, the back pressure valve 71L switches the spool 72L substantially in conjunction with the directional control valve 23 in accordance with the differential pressure between the supply and discharge lines 25A, 25B. Thus, when the hydraulic motor 32L is rotated by inertia, the back pressure valve 71L is closed, and a brake pressure is generated in the supply/discharge line 25A or the supply/discharge line 25B before and after the hydraulic motor 32L. The structure of the left back pressure valve 71L (and the right back pressure valve 71R described later) of the embodiment will be described in detail later.

The high-pressure selector valve 50 is constituted by a shuttle valve. The high-pressure selector valve 50 is provided between the supply and discharge lines 25A and 25B so as to be positioned between the hydraulic motor 32L and the back pressure valve 71L. The high-pressure selector valve 50 selects high-pressure-side pressure oil from the supply and discharge lines 25A and 25B connected to the hydraulic motor 32L, and supplies the selected pressure oil to the tilt actuator 43 via the tilt switching valve 51.

The tilt-rotation switching valve 51 is provided between the high-pressure selector valve 50 and the tilt-rotation driver 43. That is, the tilt switching valve 51 is provided in the middle of the oil passage 52 connecting the high-pressure selector valve 50 and the tilt cylinder 43A of the tilt actuator 43. The tilt-rotation switching valve 51 switches the pressure oil supplied to the tilt-rotation actuator 43. The tilt/swivel switching valve 51 is configured as a hydraulic pilot switching valve (directional control valve) having a 3-port 2 position of the hydraulic pilot portion 51A. The tilt switching valve 51 is switched between a neutral position (d) at which the oil passage 52 is connected to the drain port 54 and a drive position (e) at which the oil passage 52 is connected to the high-pressure selector valve 50, in accordance with a pilot signal (shift pilot pressure) supplied to the hydraulic pilot portion 51A.

When the tilt switching valve 51 is at the neutral position (d), the supply of the pressure oil from the high pressure selector valve 50 to the tilt cylinder 43A is cut off, and the tilt cylinder 43A communicates with the drain port 54. Thereby, the swash piston 43B is in a non-operating state, and the pressing force acting on the swash plate 42 is suppressed, and the swash plate 42 is held at a large swash position (maximum motor swash). On the other hand, when the tilt switching valve 51 is in the drive position (e), a part of the pressure oil flowing through the supply/discharge line 25A (25B) on the high pressure side selected by the high pressure selection valve 50 among the supply/discharge lines 25A and 25B is supplied to the tilt cylinder 43A through the oil passage 52. Thereby, the swash plate 42 is pressed by the swash plate 43B in an operating state, and the swash plate 42 is held at a small swash position (minimum motor swash).

The shift pilot pressure is supplied from the pilot control valve 58 to the hydraulic pilot portion 51A of the tilt switching valve 51 via the pilot pressure port 46. Here, when the shift pilot pressure required to switch the tilt switching valve 51 from the neutral position (d) to the drive position (e) acts on the hydraulic pilot portion 51A, the tilt switching valve 51 moves from the neutral position (d) to the drive position (e), and the motor tilt is minimized. In contrast, when the shift pilot pressure does not act on the hydraulic pilot portion 51A, the tilt switching valve 51 does not move to the drive position (e), and the motor tilt is still at a maximum.

The relief valves 53A and 53B are provided in the middle of the supply and discharge lines 25A and 25B so as to be positioned between the hydraulic motor 32L and the back pressure valve 71L. When the brake pressure generated in the supply/discharge line 25A or 25B during inertial rotation of the hydraulic motor 32L rises to a predetermined set pressure, the relief valves 53A and 53B open, and the excess pressure at that time is released.

That is, the relief valves 53A and 53B are provided to protect the travel drive device 31L. When the motor port pressure of one of the motor ports 47A (47B) of the pair of motor ports 47A, 47B becomes equal to or higher than a predetermined value (set pressure), the relief valves 53A, 53B cause the pressure oil to flow out to the other motor port 47B (47A). Thus, the relief valves 53A and 53B prevent the traveling drive device 31L from being damaged by high pressure.

The drain port 54 opens, for example, in the motor housing 33 of the hydraulic motor 32L. The drain port 54 drains oil (drain) leaking from a gap of a sliding portion including internal parts of the piston in the hydraulic motor 32L from the hydraulic motor 32L. The drain port 54 is connected to the hydraulic oil tank 15 via a drain line 57.

On the other hand, as shown in fig. 2, the right travel drive device 31R rotationally drives the right drive wheels based on the pressure oil supplied from the second hydraulic pump 14. The right travel hydraulic motor 32R of the right travel drive device 31R is connected to the hydraulic pump 14 and the hydraulic oil tank 15 via the right supply and discharge lines 26A and 26B. The right travel hydraulic motor 32R (hereinafter, also simply referred to as the hydraulic motor 32R) as the second hydraulic motor is rotationally driven by the pressure oil from the second hydraulic pump 14. A right travel direction control valve 24 is provided in the middle of the right supply and discharge pipes 26A, 26B. The right travel drive device 31R is the same as the left travel drive device 31L. The right travel drive device 31R (hereinafter, also simply referred to as the travel drive device 31R) is given the same reference numerals as those of the left travel drive device 31L, and the above description thereof is omitted.

In this case, the right travel drive device 31R is configured by the right travel hydraulic motor 32R and the right brake valve 44R (hereinafter, also simply referred to as the brake valve 44R). A right back pressure valve 71R (hereinafter, also simply referred to as a back pressure valve 71R) as a second back pressure valve is provided midway between the pair of supply and discharge lines 26A, 26B so as to be positioned between the right travel directional control valve 24 and the right travel hydraulic motor 32R. In the back pressure valve 71R, a right spool 72R (hereinafter, also simply referred to as a spool 72R) as a second spool is displaced in the axial direction based on the pressure difference between the supply and discharge lines 26A, 26B.

The drain line 57 connects the drain port 54 of the travel drive devices 31L and 31R (hydraulic motors 32L and 32R) and the hydraulic oil tank 15. The drain line 57 discharges drain from the travel drive devices 31L and 31R including the hydraulic motors 32L and 32R to the hydraulic oil tank 15. That is, the drain from the travel drive devices 31L and 31R flows around the hydraulic oil tank 15 via the drain line 57.

The pilot pressure control valve 58 switches the tilt switching valve 51 of the travel drive devices 31L and 31R. Therefore, the pilot pressure control valve 58 controls the pressure oil (pilot pressure) from the pilot hydraulic pump 20. That is, the pilot control valve 58 controls the shift pilot pressure supplied to the tilt switching valve 51 in order to switch the motor tilt of the travel driving devices 31L and 31R (hydraulic motors 32L and 32R). The pilot control valve 58 is, for example, a 3-port 2-position electromagnetic switching valve (electromagnetic proportional control valve) constituted by a proportional electromagnetic valve, and has an electromagnetic pilot portion 58A (solenoid).

The input side of the pilot pressure control valve 58 is connected to the pilot hydraulic pump 20 via a pilot discharge conduit 21. The output side of the pilot control valve 58 is connected to the tilt switching valve 51 (i.e., the hydraulic pilot portion 51A) via a pilot conduit 59 for gear shifting and the pilot pressure port 46 of the travel drive devices 31L and 31R. The electromagnetic pilot portion 58A of the pilot pressure control valve 58 is connected to the controller 61. The pilot control valve 58 can output pressure oil (shift pilot pressure) at a pressure corresponding to the electric power W supplied from the controller 61. On the other hand, when the electric power W is not supplied from the controller 61, the pilot pressure control valve 58 communicates the pilot pressure port 46 with the hydraulic oil tank 15 as shown in fig. 2.

The shift pilot conduit 59 is provided between the pilot pressure control valve 58 and the tilt switching valve 51 of the travel drive devices 31L and 31R. That is, the shift pilot conduit 59 is a conduit connecting the pilot control valve 58 and the tilt switching valve 51. The shift pilot conduit 59 supplies the pilot pressure from the pilot pressure control valve 58 to the tilt switching valve 51.

A tilt-turn changeover switch 60 as a capacity changeover switch (speed changeover switch) is provided in the cab 7. The tilt/turn switch 60 is connected to a controller 61. The tilt/turn switching switch 60 switches the motor capacities (controls the motor tilt/turn state) of the travel driving devices 31L and 31R (hydraulic motors 32L and 32R). That is, the operator can adjust the driving speed (rotation speed) of the travel driving devices 31L and 31R by operating the tilt change-over switch 60.

In this case, tilt/swivel changeover switch 60 has two selection positions (travel modes), for example, a low speed position (low speed mode) for causing hydraulic excavator 1 (lower traveling structure 2) to travel at a low speed and a high speed position (high speed mode) for traveling at a high speed. When the tilt/swivel switch 60 is switched to the low-speed position, the motor capacity becomes large (the tilt is large), and the hydraulic motors 32L and 32R can be rotated at a low speed. On the other hand, when the tilt-turn switching switch 60 is switched to the high-speed position, the motor capacity becomes small (the tilt is small), and the hydraulic motors 32L and 32R can be rotated at high speed.

The controller 61 is a control device that controls (electronically controls) the pilot pressure control valve 58. The controller 61 includes a microcomputer, a drive circuit, a power supply circuit, and the like. That is, the controller 61 has an arithmetic processing unit configured to include a memory such as a RAM or a ROM and a CPU, and operates according to a computer program. The input side of the controller 61 is connected to the tilt/turn changeover switch 60. The output side of the controller 61 is connected to the pilot pressure control valve 58. Electric power is supplied to the controller 61 from a battery (not shown) as a power source mounted on the upper revolving structure 4.

The controller 61 is input with the state of the tilt/turn switch 60, that is, whether the running mode (selected position) is the low speed mode (low speed position) or the high speed mode (high speed position). The controller 61 supplies the drive electric power W to the pilot pressure control valve 58, and controls the shift pilot pressure applied to the pilot pressure ports 46 of the travel drive devices 31L and 31R. For example, when it is determined that the tilt change-over switch 60 is set at a high speed position corresponding to a small tilt (high speed, low torque) of the motor, the controller 61 supplies the electric power W to the pilot control valve 58.

Thus, the controller 61 controls the pilot pressure control valve 58 according to the selected position of the tilt-turn switching switch 60. Thus, the controller 61 controls the motor capacities (motor tilt states) of the travel driving devices 31L and 31R. Specifically, when the tilt change-over switch 60 is in the high-speed position, the controller 61 supplies the electric power W to (the electromagnetic pilot portion 58A of) the pilot pressure control valve 58 so that the hydraulic motors 32L and 32R have a small capacity (high speed and low torque). On the other hand, when the tilt change-over switch 60 is in the low speed position, the controller 61 does not supply the electric power W to (the electromagnetic pilot portion 58A of) the pilot control valve 58. In this case, the hydraulic motors 32L and 32R have large capacities (low speed and high torque).

The back pressure valves 71L and 71R of the embodiment will be described below. In the following description, the left back pressure valve 71L will be mainly described, but the right back pressure valve 71R has the same configuration.

As shown in fig. 3 to 7, the back pressure valve 71L (71R) is constituted by a 6-port 5-position spring center type spool type switching valve. In the back pressure valve 71L (71R), the spool 72L (72R) is held at a neutral position a0 by a neutral spring 103. A pair of pressure chambers 104 and 105 (hereinafter, also referred to as pressure chambers 104 and 105) of the back pressure valve 71L (71R) are connected to the pair of valve ports 45A and 45B via a speed adjustment orifice 106. That is, the pressure chamber 104 of the back pressure valve 71L (71R) on one side (left side) is connected to the valve port 45A on one side (left side) via the speed adjusting orifice 106. The other (right) pressure chamber 105 of the back pressure valve 71L (71R) is connected to the other (right) valve port 45B via a speed adjustment orifice 106.

The pressures of the valve ports 45A and 45B act on the pressure chambers 104 and 105 of the back pressure valve 71L (71R). When a differential pressure (motor drive pressure) is generated between one valve port 45A and the other valve port 45B, the spool 72L (72R) is moved (displaced) in the axial direction (i.e., the left and right directions) by a thrust force based on the differential pressure between the one pressure chamber 104 and the other pressure chamber 105. The speed adjustment throttle 106 is a member that adjusts the moving speed of the spool 72L (72R), and reduces the impact at the time of departure and at the time of stop, which is caused by the excessively fast operation of the spool 72L (72R).

By the movement of the spool 72L (72R), the back pressure valve 71L (71R) can be switched among the neutral position a0, the drive position AR1, the drive position AR2, the drive position AL1, and the drive position AL 2. The neutral position a0 is a position at which the pair of (left and right) valve ports 45A and 45B and the pair of (left and right) motor ports 47A and 47B are cut off from each other. The drive position AR1 is a position at which the motor port 47A and the valve port 45A communicate with each other via the notch portion 107 serving as a throttle oil passage, and the valve port 45B and the motor port 47B are shut off from each other. The drive position AR2 is a position at which the motor port 47A and the valve port 45A communicate with each other through the full-circumference opening 108 serving as a full-circumference oil passage, the pressure chamber 105 and the valve port 45B communicate with each other through the early-return oil passage 109, and the valve port 45B and the motor port 47B are shut off from each other. In the embodiment, as described later, in the drive position AR2, the valve port 45A and the valve port 45B communicate with each other via the communication passage 73L (73R) and the orifice 74L (74R).

The drive position AL1 is a position at which the motor port 47B and the valve port 45B communicate with each other via the notch portion 107 serving as a throttle passage, and the valve port 45A and the motor port 47A are shut off from each other. The drive position AL2 is a position at which the motor port 47B and the valve port 45B communicate with each other through the full-circumference opening 108 serving as a full-circumference oil passage, the pressure chamber 104 and the valve port 45A communicate with each other through the early return oil passage 109, and the space between the valve port 45A and the motor port 47A is blocked. In the embodiment, as described later, in the drive position AL2, the valve port 45A and the valve port 45B communicate with each other via the communication passage 73L (73R) and the orifice 74L (74R). When the early return oil passage 109 is opened, the pressure oil can flow into and out of the pressure chambers 104 and 105 without passing through the speed adjustment orifice 106, and the drive positions AR2 and AL2 are used to improve the responsiveness of the spool 72L (72R).

The characteristics of the opening area of the outlet oil passage of the back pressure valve 71L (71R) will be described with reference to fig. 8. In fig. 8, a stroke X of the spool 72L (72R) and an opening area a of the outlet oil passage of the back pressure valve 71L (71R) are indicated by a solid line 65_CBThe relationship (2) of (c). When the stroke X of the spool 72L (72R) is 0(X equals 0), it corresponds to the neutral position a 0. At this time, the opening area a of the outlet oil passage of the back pressure valve 71L (71R)_CBBecomes 0 (A)_CB0). The stroke X of the spool 72L (72R) is X_Cr≤X≤X_EOCorresponds to the drive position AR1 or the drive position AL 1. At this time, the opening area A of the outlet oil passage_CBOpening area A corresponding to the opening of the notch portion 107_CBGradually increase to A_EO. The stroke X of the spool 72L (72R) is X_EO≤X≤X_FSCorresponds to the drive position AR2 or the drive position AL 2. At this time, the opening area A of the outlet oil passage_CBThe opening area is increased to the maximum opening area A in proportion to the stroke X in accordance with the opening of the entire peripheral opening 108_CBmax。X_FSMaximum stroke position X with spool 72L (72R)_FSAnd (7) corresponding.

The operation characteristics of the back pressure valve 71L (71R) will be described with reference to fig. 9. In fig. 9, a relationship between the driving pressure P of the back pressure valve 71L (71R) and the stroke X is indicated by a solid line 66. The stroke X of the spool 72L (72R) is proportional to the drive pressure P, and when the drive pressure P becomes P_Cr、P_EOWhen it is turned into X respectively_Cr、X_EOThe position of (a). If the driving pressure P becomes P_FSAbove (P is not less than P_FS) Then, the spool 72L (72R) is held at the maximum stroke position X_FS。

Next, the cranking operation of hydraulic excavator 1 will be described with reference to fig. 15 and 16. Fig. 15 is a schematic diagram of a meandering operation of a hydraulic excavator (comparative example) provided with a back pressure valve not provided with the communication passage 73L (73R) and the orifice 74L (74R) which are features of the embodiment. Here, the rotation speed of the left travel drive device 110L in fig. 15 is RL, and the rotation speed of the right travel drive device 110R is RR. The drive pressure of the left travel drive device 110L is PL, and the drive pressure of the right travel drive device 110R is PR.

During travel on a flat ground, for example, when the rotation speed RR of the right travel drive device 110R is greater than the rotation speed RL of the left travel drive device 110L (RR > RL), the right-side track 2D rotates faster than the left-side track 2D. Thus, the high-rotation right travel drive device 110R pulls the low-rotation left travel drive device 110L, and the drive pressures PL and PR of the left and right travel drive devices 110L and 110R are referred to as PR > PL. The driving pressures PL and PR affect the opening characteristics of the back pressure valves provided in the brake valves 111L and 111R. When the driving pressure PL becomes low, the oil passage on the motor side (outlet side) of the back pressure valve is reduced, and the left travel drive device 110L on the low rotation side is further decelerated. As a result, hydraulic excavator 1 tends to curve largely to the left.

Fig. 16 is a characteristic diagram showing an example of temporal changes in the rotation speeds RL and RR, the drive pressures PL and PR, and the strokes XL and XR of the comparative example. In this case, the stroke of the spool of the back pressure valve of the left travel drive device 110L is XL, and the stroke of the spool of the back pressure valve of the right travel drive device 110R is XR.

At time t1, driving pressures PL and PR of the left and right travel driving devices 110L and 110R exceed P_FSThe strokes XL, XR become the maximum stroke X_FS. Since the high-rotation right travel drive device 110R pulls the low-rotation left travel drive device 110L due to the difference in the rotation speeds of the left and right travel drive devices 110L, 110R, the right travel drive device 110R is on the pulling side and therefore becomes high pressure, and the low-rotation left travel drive device 110L is on the pulled side and therefore becomes low pressure, and a left-right difference is generated in the drive pressures PL, PR. Here, the difference between the discharge flow rate Qp1 of the first hydraulic pump 13 and the discharge flow rate Qp2 of the second hydraulic pump 14 is further increased as the oil temperature increases due to traveling.

At time t2, the balance between "pulling" and "pulled" is lost due to a running load fluctuation or the like, and the drive pressure PR rises at once and the drive pressure PL decreases. In this case, the driving pressure PL of the left travel drive device 110L is lower than P_FSThe stroke XL begins to decrease. At time t3, the drive pressure PL of the left travel drive device 110L is lower than P_EOWith travel XL reduced to X_EO. Therefore, the opening area A of the outlet oil passage of the back pressure valve on the left side_CBThe rapid decrease causes the brake to be applied to the left travel driving device 110L, and the rotation speed RL of the left travel driving device 110L rapidly decreases. This increases the difference in the rotational speed between the left and right travel drives 110L and 110R, and generates a large curve to the left. If a large curve starts to occur, the stroke X ratio X sufficient for driving the back pressure valve cannot be secured_EOLarge (X > X)_EO) Driving pressure P of (i.e. ratio P)_EOHigh driving pressure (P > P)_EO). This may cause a large meandering to continue for a long time.

In contrast, in the embodiment, the communication passages 73L and 73R are provided in the spools 72L and 72R of the left and right back pressure valves 71L and 71R, respectively. That is, in the embodiment, at the drive position AR2, the motor port 47A and the valve port 45A are communicated with each other through the full-circumference opening portion 108 serving as a full-circumference oil passage, and the pressure chamber 105 and the valve port 45B are communicated with each other through the early return oil passage 109. Further, the valve port 45B and the motor port 47B are shut off, and the valve port 45A and the valve port 45B are communicated with each other via a communication passage 73L (73R) and an orifice 74L (74R). In the drive position AL2, the motor port 47B and the valve port 45B are communicated with each other through the full-periphery opening 108 serving as a full-periphery oil passage, and the pressure chamber 104 and the valve port 45A are communicated with each other through the early-return oil passage 109. Further, the valve port 45A and the motor port 47A are shut off, and the valve port 45A and the valve port 45B are communicated with each other via a communication passage 73L (73R) and an orifice 74L (74R).

Broken line 67 in fig. 8 indicates a communication oil passage opening area a which is an opening area of communication passages 73L, 73R_CM. The communication passages 73L, 73R have a characteristic in that the stroke X is X at the drive position AR2 or AL2 of the spools 72L, 72R_CMAbove (X is not less than X_CM) Opening, stroke X at X_FSBecomes the maximum opening A_CMmax. In this case, the stroke X of the opening of the communication paths 73L and 73R_CMSet before the communication of the whole peripheral opening 108 is startedBy a stroke X_EOPosition and full range X_FSBetween positions, i.e. the specific travel X_EOLarge and less than full range X_FSSmall position (X)_EO＜X_CM＜X_FS). In addition, as shown in FIG. 9, the stroke X_CMAnd a driving pressure P_CMAnd (7) corresponding. In this case, the driving pressure P_CMRatio and stroke X_EODrive pressure P corresponding to position_EOLarge specific area and whole course X_FSDrive pressure P corresponding to position_FSSmall (P)_EO＜P_CM＜P_FS)。

Fig. 10 shows the characteristic of the communicating oil passage orifice, that is, the characteristic (orifice characteristic) of the orifices 74L, 74R of the communicating passages 73L, 73R. Here, assuming that the throttle passing flow rate Q, the throttle diameter d, the working pressure P, and the viscosity μ of the oil liquid are used, the throttle characteristics can be generally expressed by the following expressions 2 and 3. The expression 2 corresponds to the characteristics of the orifice-type orifice, and the expression 3 corresponds to the characteristics of the choke-type orifice.

[ mathematical formula 2]

[ mathematical formula 3]

Q(d，μ，p)＝Kd⁴mu.P (K: proportionality coefficient)

In the embodiment, the throttle characteristics (communication oil path throttle characteristics) of the communication paths 73L and 73R are intermediate characteristics between the throttle orifice type throttle and the choke orifice type throttle. As shown in fig. 10, the larger the throttle diameter d, the more the oil temperature increases and the viscosity μ decreases, the larger the flow rate.

Here, the larger the communication oil passage restrictor, the greater the effect of suppressing hunting, but the greater the amount of communication oil at the time of high driving pressure, which may lead to a decrease in volumetric efficiency of the driving devices 31L and 31R for running and a decrease in speed during climbing and steering. Therefore, it is necessary to select the smallest orifice capable of maintaining a sufficient meandering suppressing effect. The orifice can be selected as follows. That is, the rotation speed R of the travel drive device 31L (31R) is defined by the discharge flow rate Qp of the hydraulic pumps 13 and 14 and the capacity Vm of the hydraulic motor 32L (32R) as the above-described mathematical formula 1.

When the discharge flow rate Qp is a standard value or a maximum value Qpmax that can reflect mass production, and the capacity Vm is a standard value or a minimum value Vmmin that can reflect mass production, the rotation speed R becomes the maximum rotation speed RQ, and can be represented by the following equation 4.

[ mathematical formula 4]

When the discharge flow rate Qp is a standard value or a minimum value Qpmin that can reflect mass production, and the capacity Vm is a standard value or a maximum value Vmmax that can reflect mass production, the rotation speed R becomes the minimum rotation speed RS, and can be expressed by the following equation 5.

[ math figure 5]

The difference between the maximum rotation speed RQ and the minimum rotation speed RS is the maximum rotation speed difference generated by the mass production vehicle body. To eliminate this difference in rotation speed, it is conceivable to decrease the supply flow rate of the travel drive device 31L (31R) at the maximum rotation speed RQ 'by Δ Qt and increase the supply flow rate of the travel drive device 31R (31L) at the minimum rotation speed RS' by Δ Qt. If the rotation speeds R after Δ Qt increase and decrease are RQ 'and RS', respectively, the RQ 'and RS' can be expressed by the following expressions 6 and 7.

[ mathematical formula 6]

[ math figure 7]

To eliminate the difference in rotational speed, Δ Qt of RQ '═ RS' may be determined. That is, it can be expressed by the following equation 8.

[ mathematical formula 8]

Therefore, in order to eliminate the maximum difference in rotational speed caused by mass production of the vehicle body, the flow rate correction by the amount of 2 Δ Qt may be performed between the high-speed-side travel drive device 31L (31R) and the low-speed-side travel drive device 31R (31L).

In a construction machine (working vehicle) such as the hydraulic excavator 1, a drive pressure PmQ of the hydraulic motor 32L (32R) on the high speed side and a drive pressure PmS of the hydraulic motor 32R (32L) on the low speed side during traveling on a flat road are measured while adjusting the discharge flow rates Qp of the hydraulic pumps 13 and 14 and the capacities Vm of the hydraulic motors 32L and 32R to the maximum rotation speed differences RQ and RS generated in mass production of the vehicle body. The throttle passing flow rates QmQ and QmS when the drive pressure PmQ and the drive pressure PmS act are set so as to have the relationship of the following expression 9.

[ mathematical formula 9]

Fig. 5 shows the left back pressure valve 71L of the embodiment in a neutral position (0 position). A communication passage 73L serving as a communication oil passage is provided in the spool 72L of the back pressure valve 71L. That is, a communication passage 73L extending in the axial direction is formed inside the spool 72L. The communication passage 73L is provided with a throttle 74L made of, for example, two throttles. When the spool 72L is at the neutral position a0 (stroke X is 0), the communication oil passage between the pair of (left and right) valve ports 45A, 45B and the pair of (left and right) motor ports 47A, 47B is blocked.

FIG. 6 shows a stroke X before the communication of the entire peripheral opening 108 is started_EOThe position shows the back pressure valve 71L of the embodiment. In the X_EOPosition (stroke X ═ X)_EO) In other words between the drive position AL1 and the drive position AL2, the motor port 47B and the valve endThe oil passage between the ports 45B communicates via a notch portion 107 serving as a throttle oil passage. On the other hand, the oil passage between the valve port 45A and the motor port 47A and the communication passage 73L between the pair of (left and right) valve ports 45A, 45B are blocked.

FIG. 7 shows the maximum stroke position X_FSA back pressure valve 71L of the embodiment is shown. In the X_FSPosition (stroke X ═ X)_FS) In other words, at the drive position AL2, the oil passage between the motor port 47B and the valve port 45B communicates through the full-circumference opening 108 serving as a full-circumference oil passage. On the other hand, the oil passage between the valve port 45A and the motor port 47A is blocked, and the pair of (left and right) valve ports 45A and 45B communicate with each other via the communication passage 73L and the orifice 74L. In this way, at the drive position AR2 and the drive position AL2, the back pressure valve 71L of the embodiment causes the pressure oil of the flow rate Qt to flow between the pair of (left and right) valve ports 45A and 45B via the communication passage 73L and the orifice 74L in accordance with the drive pressure P.

As described above, according to the embodiment, the left back pressure valve 71L includes the communication passage 73L as the first communication passage, and when the displacement of the left spool 72L exceeds a predetermined amount (X) due to the pressure difference between the first and second left supply and discharge lines 25A, 25B (i.e., between the pair of valve ports 45A, 45B)_CM) The communication passage 73L communicates between the first and second left supply/discharge pipes 25A, 25B. In this case, the communication passage 73L is provided in the left spool 72L of the left back pressure valve 71L.

Similarly, as shown in fig. 2, the right back pressure valve 71R includes a communication passage 73R as a second communication passage, and when the displacement of the right spool 72R exceeds a predetermined amount (X) due to a pressure difference between the first and second right supply/discharge passages 26A, 26B_CM) The communication passage 73R communicates between the first and second right supply and discharge passages 26A, 26B. In this case, the communication passage 73R is provided in the right spool 72R of the right back pressure valve 71R.

Predetermined amount (X)_CM) That is, the displacement (stroke) of the spool 72L (72R) communicating between the supply and discharge lines 25A and 25B (26A and 26B) through the communication line 73L (73R) is set at X at which the communication of the entire peripheral opening 108 is started_EOPosition and X as maximum travel position_FSBetween the positions. I.e. a predetermined amount (X)_CM) Set in a position exceeding the notch portion 107 serving as a throttle passageThe position of (a). More specifically, when the spool 72L (72R) is displaced from the "neutral position (0)" to the ratio X_EOPosition and X_FSIntermediate positions between the positions being further X_FSX of position_CMWhen the position is "above", the supply and discharge lines 25A and 25B (26A and 26B) communicate with each other through the communication line 73L (73R). In other words, at the maximum stroke position X_FSThe supply and discharge pipes 25A and 25B (26A and 26B) are communicated with each other by a communication passage 73L (73R), but at neutral positions (0) and X_CMBetween the positions, the supply and discharge lines 25A and 25B (26A and 26B) are not communicated with each other through the communication path 73L (73R).

A first orifice 74L is provided in the middle of the communication passage 73L, and the first orifice 74L restricts the flow rate of the pressure oil flowing through the communication passage 73L. Similarly, as shown in fig. 2, a second orifice 74R is provided in the middle of the communication passage 73R, and the second orifice 74R restricts the flow rate of the pressure oil flowing through the communication passage 73R. The first and second throttles 74L and 74R are set to suppress a difference between the "flow rate of the pressure oil flowing between the first hydraulic pump 13 and the left travel hydraulic motor 32L" and the "flow rate of the pressure oil flowing between the second hydraulic pump 14 and the right travel hydraulic motor 32R" in a state where both the left travel hydraulic motor 32L and the right travel hydraulic motor 32R are rotated. That is, the first and second restrictors 74L and 74R are set to be communication flow rates that reduce the difference between the "flow rate of the pressurized oil flowing from the first hydraulic pump 13 to the left travel hydraulic motor 32L" and the "flow rate of the pressurized oil flowing from the second hydraulic pump 14 to the right travel hydraulic motor 32R" in a state where both the left travel hydraulic motor 32L and the right travel hydraulic motor 32R are rotated.

Here, as shown in fig. 5 to 7, the left back pressure valve 71L includes a housing 76, a plurality of (four) oil passages 77, 78, 79, 80, and a spool 72L. The housing 76 has a spool slide hole 75. The plurality of oil passages 77, 78, 79, and 80 are provided so as to be separated in the axial direction of the spool slide hole 75. The spool 72L is movably inserted into a spool slide hole 75 of the housing 76. The spool 72L is provided with large diameter portions 81, 82, 83 (convex portions) and small diameter portions 84, 85 (narrowed portions) adjacent to each other in the circumferential direction for communicating or blocking the oil passages 77, 78, 79, 80.

The communication passage 73L is provided in a large diameter portion 82 at an intermediate position among the three large diameter portions 81, 82, 83 of the spool 72L, that is, the large diameter portion 82 provided between the first small diameter portion 84 and the second small diameter portion 85. A communication large diameter portion 86 having a larger inner diameter than the other portions is provided at a position facing the large diameter portion 82 at the intermediate position in the radial direction in the inner peripheral surface of the spool sliding hole 75. The communication passage 73L includes a first radial passage 87, a second radial passage 88, and an axial passage 89. The first radial passage 87 opens to the first left supply and discharge passage 25A in the outer peripheral surface of the large diameter portion 82, and extends from the outer peripheral surface of the large diameter portion 82 toward the inner diameter side. When the spool 72L is displaced by a predetermined amount (X) from the neutral position toward the first left supply/discharge line 25A side_CM) The first radial passage 87 communicates with the first left supply-discharge passage 25A.

The second radial passage 88 is opened to the second left supply/discharge pipe 25B in the outer peripheral surface of the large diameter portion 82, and extends from the outer peripheral surface of the large diameter portion 82 toward the inner diameter side. If spool 72L is displaced by a predetermined amount (X) from the neutral position toward the second left supply/discharge line 25B side_CM) The second radial passage 88 communicates with the second left supply and discharge piping 25B. The axial passage 89 extends axially along the central axis of the spool 72L. The axial passage 89 connects the first radial passage 87 with the second radial passage 88. A first orifice 74L is provided in the first radial passage 87 of the communication passage 73L, and the first orifice 74L is located at a connection portion with the axial passage 89 and has a smaller inner diameter than the other portions. Further, a first orifice 74L is provided in the second radial passage 88 of the communication passage 73L, and the first orifice 74L is located at a connection portion with the axial passage 89 and has a smaller inner diameter dimension than the other portions. That is, in the embodiment, the communication path 73L is provided with a pair of first throttles 74L.

As shown in FIG. 7, if the stroke X of the spool 72L is greater than a predetermined amount (X)_CM) When the flow rate is large, the connection (communication) between the first left supply/discharge line 25A and the second left supply/discharge line 25B, between the inner peripheral surface of the spool slide hole 75 and the outer peripheral surface of the first small diameter portion 84, and between the communication large diameter portion 86 of the spool slide hole 75 and the outer peripheral surface of the first small diameter portion 84 is established via the communication path 73L. Further, a brake oil passage 90 is provided in a portion of the housing 76 that faces the large diameter portion 82 at the intermediate position of the spool 72L. Brake oil path 90 and drive device for travelingThe oil chamber (not shown) of the parking brake device of the set 31L is connected. When pressure oil (parking brake release pressure) is supplied to an oil chamber (cylinder) of the parking brake device through the brake oil passage 90, the brake (braking) of the parking brake device is released. The right back pressure valve 71R has the same configuration as the left back pressure valve 71L, and therefore, the description thereof is omitted.

The hydraulic excavator 1 according to the embodiment has the above-described configuration, and the operation thereof will be described below.

When an operator boarding the cab 7 starts the engine 12, the engine 12 drives the hydraulic pumps 13, 14, and 20. Accordingly, the pressure oil discharged from the hydraulic pumps 13 and 14 is discharged toward the traveling hydraulic motors 32L and 32R, the swing hydraulic motor, the boom cylinder 5D, the arm cylinder 5E, and the bucket cylinder 5F of the working device 5 in accordance with the lever operation and the pedal operation of the traveling operation devices 28 and 29 and the working lever operation device provided in the cab 7. As a result, hydraulic excavator 1 can perform the traveling operation of lower traveling structure 2, the revolving operation of upper revolving structure 4, the excavation operation of work implement 5, and the like.

Here, fig. 11 is a schematic diagram of suppressing the hunting operation of the working vehicle (hydraulic excavator 1) according to the embodiment. The contents related to the schematic diagram of the meandering operation of the comparative example shown in fig. 15 will be described.

When the rotation speed RR of the right travel drive device 31R is greater than the rotation speed RL of the left travel drive device 31L (RR > RL) during traveling on flat terrain, the high-rotation right travel drive device 31R pulls the low-rotation left travel drive device 31L, and the drive pressures PL and PR of the left and right travel drive devices 31L and 31R have a relationship of PR > PL. At this time, the flow rates QtL and QtR passing through (the throttles 74L and 74R of) the communication passages 73L and 73R in the brake valves 44L and 44R of the left and right travel driving devices 31L and 31R are in a relationship of QtR > QtL. That is, the flow rate of the right travel hydraulic motor 32R supplied to the high-rotation right travel drive device 31R is reduced to be equivalent to (QtR to QtL) with respect to the low-rotation left travel drive device 31L. This causes the rotation speed difference (RR-RL) to fluctuate in a direction to decrease, thereby suppressing hunting of the travel of the hydraulic excavator 1.

FIG. 12 shows an embodimentCharacteristic diagrams of examples of temporal changes in the rotational speeds RL and RR, the drive pressures PL and PR, the strokes XL and XR, and the communication flow rates QtL and QtR. The contents related to the characteristic diagram of fig. 16 will be described. At time t0, hydraulic excavator 1 starts. As the vehicle starts, the rotational speeds RL, RR and the drive pressures PL, PR increase. At time t1, the driving pressures PL and PR of the left and right travel driving devices 31L and 31R exceed P_CMThe strokes XL, XR of the back pressure valves 71L, 71R are the opening stroke positions of the communication passages 73L, that is, the communication oil passage opening stroke X_CM. Thus, the communication passages 73L, 73L of the spools 72L, 72R are opened, and the pressure oil communication between the valve ports 45A, 45B of the flow rates QtL, QtR is started in the left and right travel driving devices 31L, 31R, respectively.

At time t2, the driving pressures PL and PR of the left and right travel driving devices 31L and 31R exceed P_FSThe strokes XL, XR of the back pressure valves 71L, 71R become the maximum strokes X_FS. Due to the difference in the rotational speed between the left and right travel driving devices 31L, 31R, the high-rotation right travel driving device 31R pulls the low-rotation left travel driving device 31L, the high-rotation right travel driving device 31R is on the pulling side and thus becomes high pressure, and the low-rotation left travel driving device 31L is on the driven side and thus becomes low pressure, and a left-right difference is generated in the driving pressures PL, PR.

Here, as described above, the flow rates QtL, QtR of the communication passages 73L, 73R (the throttles 74L, 74R) in the brake valves 44L, 44R change in accordance with the drive pressures PL, PR, and function so that the rotation speed difference (RR-RL) becomes small. Therefore, the difference in rotational speed can be reduced without causing a large difference in rotational speed as in the comparative example. Accordingly, the effects of "pulling" and "being pulled" by the left and right travel driving devices 31L and 31R are reduced, and the difference between the driving pressures PL and PR is smaller than that in the comparative example.

Even if the difference between the discharge flow rate Qp1 of the first hydraulic pump 13 and the discharge flow rate Qp2 of the second hydraulic pump 14 is further increased, the flow rate difference between the communication passages 73L and 73R (orifices 74L and 74R) is increased in accordance with the increase in the difference between the drive pressures PL and PR, and the straight-ahead correction is performed. Therefore, the difference in rotation between the left and right travel drives 31L and 31R does not increase.

At time t3, the balance of "pulled" and "pulled" is lost due to sudden flow fluctuation and traveling load fluctuation of the first hydraulic pump 13, and the drive pressure PR rises at a burst and the drive pressure PL decreases. In this case, the driving pressure PL of the left travel drive device 31L is lower than P_FSThe stroke XL of the left back pressure valve 71L starts to decrease.

At time t4, the drive pressure PL of the left travel drive device 31L is lower than P_CMThe stroke XL of the left back-pressure valve 71L is reduced to X_CM. Therefore, the communication passage 73L in the left spool 72L is blocked, and the pressure oil communication amount, that is, the flow rate QtL, passing through the valve ports 45A and 45B of the left travel driving device 31L becomes 0(QtL is 0). Thus, the pressure oil in an amount not flowing into the left travel hydraulic motor 32L due to the communication between the valve ports 45A and 45B is supplied to the left travel hydraulic motor 32L, and the rotation speed RL of the left travel drive device 31L is increased. As a result, the difference between the flow rates QtL, QtR passing through the communication passages 73L, 73R (the restrictors 74L, 74R) in the left and right brake valves 44L, 44R becomes large, and therefore the straight advance correcting action becomes further large.

Regardless of the effect of the above-described straight-ahead correction, at time t5, the drive pressure PL of the left travel drive device 31L is lower than P_EO. In this case, the stroke XL of the left back pressure valve 71L is reduced to X_EOTherefore, the opening area A of the outlet oil passage of the left back pressure valve 71L_CBThe sudden decrease causes the brake to be applied to the left travel driving device 31L, and the rotation speed RL of the left travel driving device 31L decreases. On the other hand, since the right travel drive device 31R pulls the decelerated left travel drive device 31L, the drive pressure PR rises further. Therefore, the flow rate QtR of the communication passage 73R (the throttle 74R) in the brake valve 44R of the right travel driving device 31R is further increased, and the difference between the flow rates QtL and QtR of the communication passages 73L and 73R (the throttles 74L and 74R) in the brake valves 44L and 44R of the left and right travel driving devices 31L and 31R is increased, so that the effect of the straight-ahead correction is further increased than at the time t 4.

Thus, the larger the difference between the driving pressures PL and PR of the left and right travel driving devices 31L and 31R, the larger the difference between the driving pressures PL and PR, the communication passage 7 in the brake valves 44L and 44R is passedThe larger the difference between the flow rates QtL and QtR of 3L and 73R (the dampers 74L and 74R), the larger the correction action of the straight advance. Therefore, in the comparative example, the stroke X of the meandering which continues to be large for a long time, that is, the stroke X is larger than X_EOSmall state (X < X)_EO) The rotation speed difference and the driving pressure difference also act in a direction to decrease, and it is possible to suppress continuation of a large meandering for a long time.

At time t6, the drive pressure PL of the left travel drive device 31L exceeds P_EOOpening area a of the outlet oil passage of the left back pressure valve 71L_CBThe deceleration caused by the reduction of (b) is eliminated. At time t7, the driving pressures PL and PR of the left and right travel driving devices 31L and 31R exceed P_FSThe strokes XL, XR of the back pressure valves 71L, 71R become the maximum strokes X_FS. The difference in the flow rates QtL, QtR passing through the communication passages 73L, 73R (the dampers 74L, 74R) in the brake valves 44L, 44R is small, and the straight advance correcting action is reduced. Through the above-described series of operations, the difference in the rotational speed between the left and right travel drives 31L and 31R is suppressed to be smaller than that in the comparative example, and meandering of the travel of the work vehicle (hydraulic excavator 1) can be suppressed.

As described above, according to the embodiment, if the displacement of the first spool 72L of the first back pressure valve 71L exceeds the predetermined amount (X)_CM) The first communication path 73L communicates the first and second supply/discharge paths 25A and 25B. Therefore, the first communication path 73L does not always communicate between the first supply/discharge path and the second supply/discharge paths 25A and 25B (the opening is constant), but communicates with the first back pressure valve 71L in an interlocking manner (the opening is changed). Further, if the displacement of the second spool 72R of the second back pressure valve 71R exceeds a predetermined amount (X)_CM) The second communication passage 73R communicates between the third and fourth supply and discharge passages 26A, 26B. Therefore, the second communication passage 73R does not always communicate between the third and fourth supply and discharge passages 26A, 26B (the opening is constant), but communicates in conjunction with the second back pressure valve 71R (the opening changes). Therefore, when a difference in rotation speed occurs between the first hydraulic motor 32L and the second hydraulic motor 32R (during hunting), the rotation speed of the high-rotation-side travel drive device 31L (31R) can be decreased, and the rotation speed of the low-rotation-side travel drive device 31R (31L) can be increased. Therefore, the correction of the synchronous rotation speed can be fully exertedThe positive effect (correction effect of straight ahead) can suppress hunting of the running due to the difference in the rotational speed.

In this case, since the bypass throttle circuit is not used, the increase in the motor discharge pressure can be suppressed. This reduces the occurrence of a problem due to an increase in the motor relief pressure. Further, since the piping does not need to be newly provided, an increase in cost can be suppressed. The supply and discharge passages 25A, 25B, 26A, and 26B communicate with each other (along with displacement of the spools 72L and 71R) in accordance with the stroke of the back pressure valves 71L and 71R (more specifically, only the maximum stroke X)_FSTime-on), it is possible to suppress the influence on the braking performance and the starting performance of the travel drive devices 31L and 31R. This makes it possible to suppress meandering of travel due to a difference in the rotational speed between the travel drive device 31L (first hydraulic motor 32L) on one side (left side) and the travel drive device 31R (second hydraulic motor 32R) on the other side (right side) at an appropriate timing while suppressing complication of the structure and increase in cost.

According to the embodiment, the first communication passage 73L is provided in the first spool 72L of the first back pressure valve 71L, and the second communication passage 73R is provided in the second spool 72R of the second back pressure valve 71R. Therefore, the communication passages 73L and 73R can be provided by changing the spools (machining the spools) of the back pressure valves 71L and 71R according to the conventional configuration. Therefore, there is no need to newly provide parts, and this aspect can also suppress an increase in cost. In addition, the travel drive devices 31L and 31R can be prevented from increasing in size.

According to the embodiment, the first orifice 74L is provided in the middle of the first communication passage 73L, and the second orifice 74R is provided in the middle of the second communication passage 73R. The first and second restrictions 74L and 74R are set so as to suppress a difference between the flow rate of the pressure oil flowing between the first hydraulic pump 13 and the first hydraulic motor 32L and the flow rate of the pressure oil flowing between the second hydraulic pump 14 and the second hydraulic motor 32R in a state where both the first hydraulic motor 32L and the second hydraulic motor 32R are rotated. Therefore, a difference between the flow rate of the pressure oil flowing from the first hydraulic pump 13 to the first hydraulic motor 32L and the flow rate of the pressure oil flowing from the second hydraulic pump 14 to the second hydraulic motor 32R can be suppressed, and a difference in the rotational speed between the first hydraulic motor 32L and the second hydraulic motor 32R can be suppressed. In this case, the reduction in efficiency due to the communication passages 73L and 73R can be suppressed to the minimum by the throttles 74L and 74R. Moreover, a throttle capable of ensuring synchronization of the rotational speeds (a throttle capable of ensuring straightness) can be selected in advance and mounted on the driving devices 31L and 31R for traveling. Therefore, calibration on the machine on which the travel drive devices 31L and 31R are mounted, for example, calibration on the construction machine (hydraulic excavator 1) is not necessary, and the work can be simplified.

In the embodiment, a case where the communication passages 73L and 73R are provided in the spools 72L and 72R of the back pressure valves 71L and 71R has been described as an example. However, the present invention is not limited to this, and a communication passage 92 may be provided between the spool slide hole 91 and the spool 93 as in the modification shown in fig. 13 and 14, for example. That is, in the modification, a communication passage 92 and an orifice 94 as communication oil passages are provided between the spool slide hole 91 and the outer peripheral surface of the spool 93. The communication passage 92 and the orifice 94 are constituted by a groove portion 92A provided on the outer peripheral surface of the outer peripheral surface (the large diameter portion 93A at the intermediate position) of the spool 93 and an annular orifice 94A serving as an annular orifice.

As shown in fig. 13, when the spool 93 is at the neutral position a0, that is, when the stroke X is equal to 0, the communication passage 92 and the orifice 94 are blocked. As shown in fig. 14, the valve spool 93 is at the maximum stroke position X_FSCorresponding drive position AL2, i.e. stroke X ═ X_FSAt this time, the left and right valve ports 45A and 45B communicate with each other via the communication passage 92 and the orifice 94. In the modification, at the drive positions AL2 and AR2, the back pressure valve 95 causes the pressure oil at the flow rate Qt to flow between the left and right valve ports 45A and 45B via the communication passage 92 and the orifice 94 in accordance with the drive pressure P. This can suppress hunting of the vehicle caused by the difference in the rotational speed.

In the embodiment, a case where the communication oil passages 73L and 73R and the throttles 74L and 74R are provided in the spools 72L and 72R of the back pressure valves 71L and 71R is described as an example. However, the present invention is not limited to this, and for example, a communication passage and a throttle may be provided on the housing side (the housing side) of the back pressure valve, and the communication passage may be opened or closed in accordance with the operation of the back pressure valve. For example, the communication passage and the orifice may be provided independently of the back pressure valve. When the communication passage and the orifice are provided independently of the back pressure valve, the communication passage and the orifice are configured to be opened or closed in conjunction with (the spool of) the back pressure valve. Further, the orifice may be omitted, and only the communication passage may be provided.

In the embodiment, the case where the hydraulic motors 32L and 32R are axial piston swash plate hydraulic motors has been described as an example. However, the present invention is not limited to this, and other types of variable displacement hydraulic motors such as a bent axis type hydraulic motor and a radial piston type hydraulic motor may be used as the hydraulic motor. Instead of the variable displacement hydraulic motor, a fixed displacement hydraulic motor may be used. Other types of hydraulic pumps may be used for the hydraulic pumps 13 and 14, and a fixed displacement type may be used.

In the embodiment, a description has been given of an example in which the hydraulic motor for traveling is used to drive the drive wheels 2B of the track belt 2D. That is, in the embodiment, the hydraulic drive device for traveling the lower traveling structure 2 is described as an example of the hydraulic drive device. However, the hydraulic motor is not limited to this, and a hydraulic motor that drives a driving object other than the driving wheels 2B may be used. That is, the hydraulic drive device is not limited to a hydraulic drive device for traveling of a construction machine (work vehicle) such as the hydraulic excavator 1, and can be widely used as various hydraulic drive devices incorporated in, for example, an industrial machine and a general machine.

Description of the symbols

11-a hydraulic circuit (hydraulic drive device), 13-a first hydraulic pump, 14-a second hydraulic pump, 15-a working oil tank, 23-a left-travel directional control valve (first directional control valve), 24-a left-travel directional control valve (second directional control valve), 25A-a first left supply and discharge line (first supply and discharge passage), 25B-a second left supply and discharge line (second supply and discharge passage), 26A-a first right supply and discharge line (third supply and discharge passage), 26B-a second right supply and discharge line (fourth supply and discharge passage), 32L-a left-travel hydraulic motor (first hydraulic motor), 32R-a right-travel hydraulic motor (second hydraulic motor), 71L-a left backpressure valve (first backpressure valve), 71R-a right backpressure valve (second backpressure valve), 72L-a left spool backpressure (first spool), 72R-a right spool (second spool), 73L-a left communication passage (first communication passage), 73R — the right communication passage (second communication passage), 74L — the first throttle, 74R — the second throttle, 92-the communication passage (first communication passage, second communication passage), 93-the spool (first spool, second spool), 94-the throttle (first throttle, second throttle), 95-the back pressure valve (first back pressure valve, second back pressure valve).